There is a growing need for evidence to support clinical decision making in rehabilitation. Advancements in neuroimaging are essential for the support and refinement of rehabilitative interventions. Near-infrared spectroscopy (NIRS) is an emerging functional neuroimaging technique with advantages, relative to functional magnetic resonance imaging (fMRI) of portability. NIRS has the potential to be an effective neurorehabilitation outcome measure. It is an optical neuroimaging modality that indirectly monitors local fluctuations in cortical hemoglobin oxygenation, which change with neural activity. It is portable, non-invasive and allows for comparatively free movement within a natural environment. Therefore, NIRS may be a useful instrument to track neural recovery and explore neural plasticity if determined to be reliable and valid. Previous studies examining the reliability of NIRS report moderate to strong correlations (ICC = 0.5- 0.83) with fMRI in a variety of populations and cortical regions. NIRS validity studies have demonstrated equally robust results. These studies used task or stimulus-based paradigms such as hand movements, speech production or passive observation of visual stimulus. One of the most promising paradigms in human neuroimaging is the study of slow (<0.1 Hz) fluctuations in the fMRI blood-oxygen level dependent (BOLD) signal. Strong temporal correlations among neural systems exist in the absence of an overt task. This spontaneous activity (i.e. resting state) refers to activity that is not attributable to specific inputs or oututs;it represents activity that is intrinsically generated by the brain. As there is no task, studies can e conducted in people unwilling or unable to adhere to task paradigms and may circumvent concerns about differences in task performance, mirror movement, head motion, or task strategy. Resting-state fMRI data has been shown to be remarkably consistent across session in healthy individuals, implying that network analysis would be useful in following longitudinal treatment-related manipulations. Repeatability of resting state functional connectivity maps have been examined using NIRS. Evidence to support their utility have been based upon a limited sample size (n=5). Our study will use structural equation modeling (SEM) to evaluate the reliability and repeatability in effective connectivity of the visual and motor networks in patient with stroke. We will test the hypotheses that 1) fNIRS timecourses will be reliable in people with stroke and able-bodied controls within one seven-minute session and between two sessions conducted 7 days apart, and 2) there will be significant association between the fNIRS effective connectivity maps and the fMRI effective connectivity maps in people who suffered stroke greater than 12 months and in able-bodied controls The expected findings will confirm that resting-state NIRS connectivity maps can be reliably obtained in people with stroke;thus permitting future application of resting state NIRS to provide imaging metrics, in addition to behavioral outcomes, by which competing therapies may be evaluated.

Public Health Relevance

The mission of the Atlanta VA Rehabilitation Research and Development Center is to improve the function, independence, and quality of life of aging veterans with disabilities and those acquiring disabilities as they age. The mission will be accomplished by research directed towards understanding the mechanisms underlying impairments and disabilities, and applying this understanding to the design, testing, and evaluation of creative rehabilitative interventions. Mapping resting-state brain networks allows insight into the brain's functional architecture. The broad, long term objectives of the proposed project are to help monitor outcomes, develop creative rehabilitation interventions and assistive technologies for aging veterans. If the aims of the applications are achieved, we expect to find that cortical connectivity maps generated using FNIRS are both reliable and valid in stroke survivors post injury. The expecting findings will advance the scientific knowledge of brain connectivity during the resting state using FNIRS for the first time.